1. Field of the Invention
The present invention relates to keyboard switches and more particularly to electrode patterns for such switches.
2. Description of the Prior Art
FIG. 1A shows a pattern for the lower electrode of a typical keyboard switch. An insulating sheet 1 made of an insulation material such as polyimide or the like has a plurality of lower electrodes 2 formed on the surface thereof at given distances by means of printing or the like. Each lower electrode 2 is formed by a pair of interfitted electrodes 2a and 2b shaped to resemble the teeth of a comb, which are arranged at a given distance.
As shown in FIG. 1A, the electrodes 2a of three lower electrodes 2 in the first line in the upper part of the insulating sheet 1 are interconnected and led to a terminal 4.sub.1 through a lead conductor 3.sub.1. In a similar manner, the electrodes 2a in the second and third lines are interconnected and led to terminals 4.sub.2 and 4.sub.3 through lead conductors 3.sub.2 and 3.sub.3, respectively.
On the other hand, the three electrodes 2b in the first column in the left part of the insulating sheet 1 are interconnected and led to a terminal 4.sub.4 through a lead conductor 3.sub.4. In a similar manner, the three electrodes 2b in the second and third columns are interconnected and led to terminals 4.sub.5 and 4.sub.6 through lead conductors 3.sub.5 and 3.sub.6, respectively.
FIG. 1B shows an upper-electrode pattern of the conventional keyboard switch. In the Figure, an insulating sheet 5 made of an insulation material such as polyimide or the like has rectangular upper electrodes 6 formed on the surface thereof in positions to face the lower electrodes 2 formed on the lower-electrode insulating sheet 1. The upper electrodes 6 cover the same general surface area as the lower electrodes 2.
The above-mentioned insulating sheets 1 and 5 are stacked, one upon the other with the lower electrodes 2 and the upper electrodes 6 made to face each other through spacers 7, as shown in FIG. 2A which is a sectional view of a part of a keyboard switch.
In addition, an insulation board 8 supports the lower-electrode insulating sheet 1.
In operation, by downwardly pressing the portion of the upper-electrode insulating sheet 5 on the side opposite to the side of the upper electrodes 6, the portion therebelow is deflected between the spacers 7 as shown in FIG. 2B. Contact of an upper electrode 6 with the teeth of the electrode 2 permits the electrodes 2a and 2b to conduct, thereby allowing a desired output to be led from the terminal 4.
The upper electrodes 6 for the conventional keyboard switch described above are disposed on the upper-electrode insulating sheet 5 at positions corresponding to the lower electrodes 2, and a decorative sheet or pattern is printed at P on the upper surface as the sheet 5 to provide an operation surface of the keyboard switch. Since the upper electrodes 6 must correspond to the patterns formed on the decorative sheet, different upper-electrode patterns are needed so as to correspond to decorative sheets of a variety of products. Consequently, it is necessary to increase the number of electrode patterns corresponding to a variety of products, so that design control becomes complicated.